U.S. patent number 3,961,908 [Application Number 05/446,412] was granted by the patent office on 1976-06-08 for autoclave system for leaching sulfide concentrates.
This patent grant is currently assigned to Freeport Minerals Company. Invention is credited to Freddie J. Touro.
United States Patent |
3,961,908 |
Touro |
June 8, 1976 |
Autoclave system for leaching sulfide concentrates
Abstract
A method and apparatus for high temperature-high pressure acid
leaching of sulfide ores is described. The apparatus includes an
autoclave having a plurality of pressurized compartments and a
water removing-heat removing condenser. Means are described for the
introduction of a neutralizing agent directly into the autoclave in
order to maintain the acidity of the slurry at a level where
substantially all of the iron present in the slurry will form an
insoluble iron oxide precipitate. Means are described for removing
the gaseous products resulting from the introduction of the
neutralizing agent while avoiding contamination thereby of a
substantial portion of the oxygen.
Inventors: |
Touro; Freddie J. (New Orleans,
LA) |
Assignee: |
Freeport Minerals Company (New
York, NY)
|
Family
ID: |
23772471 |
Appl.
No.: |
05/446,412 |
Filed: |
February 27, 1974 |
Current U.S.
Class: |
422/269;
423/35 |
Current CPC
Class: |
C22B
3/00 (20130101); Y02P 10/20 (20151101); Y02P
10/234 (20151101) |
Current International
Class: |
C22B
3/00 (20060101); B01J 003/04 (); C01G 003/02 ();
C22B 015/00 () |
Field of
Search: |
;23/290,263,286,267R,267A,267B,267C,267D,267E,267F,267MS,267S,269
;75/101,117,119 ;423/150,27 ;210/15,63,201,218 ;266/12 ;202/158
;203/DIG.6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Scovronek; Joseph
Attorney, Agent or Firm: Schapira; Ronald A.
Claims
I claim:
1. Apparatus for the leaching of ores comprising:
a horizontally disposed autoclave having means for establishing a
predetermined normal liquid level and a vapor space above the
liquid level in said autoclave,
means for supplying a slurry of ore into said autoclave,
upstanding baffle means within said autoclave, disposed along the
horizontal length of said autoclave and dividing said autoclave
into at least three compartments, which include an upstream
compartment, a downstream compartment, and a compartment
intermediate said upstream and downstream compartments,
said baffle means further comprising upper edges above the
predetermined normal liquid level in said autoclave which allow
overflow movement of said slurry between said compartments during
operation of said autoclave,
means isolating the vapor space above said intermediate compartment
from the vapor space above said upstream and downstream
compartments,
means interconnecting the vapor space above said upstream and
downstream compartments whereby vapor can move freely between said
upstream and downstream compartments but cannot enter said isolated
vapor space above said intermediate compartment,
means for supplying an oxygen-containing gas into said autoclave
other than in said isolated vapor space,
means for agitating and intermixing said slurry with said
oxygen-containg gas,
means for maintaining the temperature of said slurry within said
autoclave,
means for maintaining the pressure of said oxygen-containing gas
within said autoclave,
means for introducing a neutralizing agent into said intermediate
compartment so that gaseous reaction products of said neutralizing
agent and said slurry are contained within said isolated vapor
space above said intermediate compartment,
means for removing said gaseous reaction products from said
isolated vapor space while avoiding contamination of said
oxygen-containing gas with said gaseous reaction products,
means for purging nonreacted gases from said upstream and
downstream compartments, and
means for continuously withdrawing a stream of product slurry from
said autoclave.
2. Apparatus as defined in claim 1 wherein said means for isolating
said vapor space above said intermediate compartment comprises a
pair of downwardly extending baffle means, about said intermediate
compartment, the lower edges of which extend below the
predetermined normal liquid level in said autoclave.
3. Apparatus as defined in claim 1 wherein the said means
interconnecting the vapor space above said upstream and downstream
compartments comprises an open-ended conduit which bypasses said
isolated vapor space.
4. Apparatus as defined in claim 1 wherein the means for
maintaining the temperature of said slurry within said autoclave
comprise
conduit means for withdrawing a stream of high temperature vapor
from a vapor space of said autoclave other than said isolated vapor
space,
a condenser connected to said conduit means to condense at least a
portion of said high temperature vapor,
means for discharging the condensate to waste,
and means for returning the uncondensed portion of said high
temperature vapor to a vapor space of said autoclave other than
said isolated vapor space.
5. Apparatus as defined in claim 1 wherein said autoclave contains
more than three compartments.
6. Apparatus as defined in claim 1 wherein said autoclave contains
at least one compartment disposed between said upstream and
intermediate compartments.
7. Apparatus as defined in claim 1 wherein said autoclave contains
at least one compartment, disposed between said upstream and
intermediate compartments, having a vapor space above it that
interconnects with the vapor spacae above said upstream compartment
but is not interconnected with said isolated vapor space above said
intermediate compartment.
8. Apparatus of claim 2 wherein said means for agitating and
intermixing said slurry with said oxygen-containing gas comprises
an agitator in each compartment below the predetermined normal
liquid level in said autoclave.
9. Apparatus of claim 8 wherein said autoclave is cylindrically
shaped.
Description
BACKGROUND OF THE INVENTION
This invention relates to the recovery of non-ferrous metals from
sulfide ores containing nickel, cobalt, copper and other nonferrous
metals, and more particularly, it relates to the recovery of these
metals from sulfide ore concentrates by the acidic leaching of
these concentrates in the presence of oxygen at high temperatures
and pressures. Specifically, this invention relates to the
oxidative leaching of iron-containing sulfide ores, such as
chalcopyrites, at high temperatures and pressures wherein
neutralizing agents are employed to neutralize at least a portion
of the free acid present in the concentrate slurry being
processed.
In existing autoclave processes for the high temperature-high
pressure treatment of sulfide ore concentrates for the recovery of
metal values by oxidative leaching it is often desirable to
neutralize a portion of the acidity produced as a result of the
reactions that take place in the process. Normally, alkaline-earth
metal neutralizing agents, such as lime or limestone, are used for
this purpose. In some instances this neutralization is carried out
after the oxidation-leaching step in a vessel separate from that of
the main oxidation-leaching reaction. In other instances the slurry
is removed from the autoclave, neutralized with the lime or
limestone, and then returned to the autoclave for further
processing. Alternatively, the neutralizing agent may be added
directly to the leaching vessel. The neutralization of oxidized
sulfide slurries with lime or limestone is described in U.S. Pat.
Nos. 2,686,114 and 2,718,455.
Because of cost considerations, limestone is usually the preferred
neutralizing agent. When limestone is used, however, carbon dioxide
is produced which tends to dilute the gases that are used for
oxidation. In order to prevent a buildup of CO.sub.2 in the system
the CO.sub.2 must be bled off. Since the CO.sub.2 is distributed
throughout the vapor space of the autoclave system, this bleeding
is accompanied by losses of valuable oxygen. Likewise, it is
usually necessary in these processes to control the prescribed
operating temperatures, which, as a result of the exothermic nature
of the oxidation reactions, tend to rise quite rapidly. In order to
do this it then becomes necessary to remove heat from the system.
This is commonly done by venting the vapors to the atmosphere with
the consequent loss of the oxygen present in the vapors. Still in
other instances the slurry is removed from the autoclave, cooled in
a separate operation, and then returned to the autoclave system.
Such methods are for the most part inefficient and wasteful and are
not without a number of disadvantages.
It is the object of this invention to provide an autoclave system
for the effective oxidation-leaching of sulfide ore concentrates
without the disadvantages associated with conventional autoclave
systems which have been used heretofore for the treatment of these
concentrates.
BRIEF SUMMARY OF THE INVENTION
The autoclave system of this invention involves a horizontal,
cylindrical pressure vessel fitted internally with baffles forming
a plurality of compartments. One compartment is provided with two
auxiliary baffles, the lower edges of which are submerged beneath
the normal liquid level so that the vapor space above the liquid
level of this compartment is isolated from the vapor space above
the liquid in the other compartments. An open-ended conduit
connects the common vapor spaces of the other compartments.
Means are provided for continuously feeding a sulfide ore slurry
into the autoclave. An oxygen-containing gas is continuously fed
into the autoclave to react with the slurry and form a solution of
nonferrous sulfates.
Means are provided for introducing a neutralizing agent into the
compartment provided with the isolated vapor space to maintain the
acid concentration of the slurry at a level where substantially all
of the iron present in the slurry will precipitate as insoluble
iron oxide (Fe.sub.2 O.sub.3). Conduit means are provided for
removing from this compartment any gaseous product formed by the
reaction of the neutralizing agent with the slurry while avoiding
contamination of the vapor in the remaining compartments of the
autoclave with the gaseous product.
A water-cooled condenser is also provided which is used to maintain
the temperature within the vessel at a predetermined level. This
condenser permits the removal of heat and water vapor from the
autoclave without loss of valuable oxygen from the system.
These and other aspects of my invention will be understood more
thoroughly in the light of the following description, as
illustrated by the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a schematic representation of the autoclave used in
my invention and also serves as a flow sheet of the system
according to the invention.
DETAILED DESCRIPTION
A horizontal, cylindrically-shaped pressure vessel or autoclave,
generally designated 10, is fitted internally with five upstanding
lower baffles 12, the upper edges of which extend avove the
predetermined normal liquid level maintained in said autoclave. The
baffles 12 form six compartments 10A, 10B, 10C, 10D, 10E and 10F
within the autoclave. An agitator 14, driven by a motor, not shown,
is placed in the lower portion of each compartment and below the
normal liquid level thereof. A pair of upper baffles 16, 18 extend
downwardly so that the lower edges thereof are submerged beneath
the normal liquid level. An open-ended conduit 20 extends through
baffles 16, 18 and connects the vapor space above the liquid level
of compartments 10A, 10B, 10C with the vapor space above
compartments 10E and 10F. The vapor space 22 above the liquid level
of compartment 10D is isolated from the vapor space above each of
the other compartments.
In the preferred embodiment of the invention the system is employed
in the high temperature-high pressure oxidation-acid leaching of a
chalcopyrite (CuFeS.sub.2) concentrate.
A continuous feed of chalcopyrite slurry enters compartment 10A
through conduit 24 and a continuous flow of an oxygen-containing
gas is fed into the autoclave 10 through conduit 26. The slurry
feed stream 24 may consist of water and concentrate, or dilute
H.sub.2 SO.sub.4 and concentrate, or recycle slurry streams and
concentrate, depending on process considerations. If desired, the
water, dilute H.sub.2 SO.sub.4 or recycle slurry streams could be
fed into the autoclave separately from the chalcopyrite
concentrate. The oxygen content of the oxygen-containing gas may
vary widely. Because of economic considerations, however, it is
preferred that a technical grade oxygen-containing gas having more
than 95% by volume O.sub.2 be used.
The point of introduction of the oxygen-containing gas into the
autoclave is not critical. It can be anywhere except in compartment
10D having the isolated vapor space. Preferably the
oxygen-containing gas is introduced at one end of the autoclave. In
some cases it may be desirable to have more than one point of
injection of the oxygen-containing gas. For example, the
oxygen-containing gas could be injected below the surface of the
slurry in each compartment, except the compartment having the
isolated vapor space. In such a case the injection of the gas could
be used as the means for agitating the slurry and mechanical
agitation could then be minimized or eliminated. Total pressure
within the autoclave should be maintained between about 300 and
1000 psig, and preferably between about 400 and 600 psig. The
quantity of oxygen supplied should be sufficient to react with and
oxidize all of the copper and iron in the slurry fed to the
autoclave.
The slurry is agitated by agitators 14 and this results in contact
between the slurry and the oxygen atmosphere which than causes the
chalcopyrite to be oxidized to CuSO.sub.4 and FeSO.sub.4 with the
evolution of heat according to the following equation, which takes
place in an acid medium:
Agitation of the slurry by either the agitators 14, or the
introduction of oxygen, or both, together with the continuous feed
of slurry into the autoclave through conduit 24 will cause the
slurry to flow from compartment 10A over baffle 12 to compartment
10B, from compartment 10B over baffle 12 to compartment 10C. Flow
of the slurry from compartment 10C to compartment 10D will be under
the lower edge of baffle 16 and over the upper edge of baffle 12.
Flow from compartment 10D to 10E will be over baffle 12 and under
baffle 18, and flow will then continue from one compartment to the
next over baffle 12.
As the slurry flows consecutively through compartments 10A, 10B and
10C reaction (1) continues as well as the following reactions which
result in the precipitation of iron as hematite (Fe.sub.2 O.sub.3)
and the production of additional acid:
and
as noted in equation (1), heat is generated in the autoclave.
Therefore the heat in excess of that required to maintain the
desired slurry temperature, which in these processes is normally
between about 350.degree. and 450.degree.F, must be removed. This
removal of heat is accomplished by removing a stream of vapor
composed of water vapor, oxygen, and nitrogen through conduit 28.
This stream enters condenser 30 where water vapor is condensed on
the outside of tubes 32 by a cooling medium such as water which is
circulated from a source, not shown, through the inside of the
tubes. If desired, as for example, where corrosion is a factor,
condenser 30 could be constructed to have the water vapor condense
on the inside of the condenser tubes and the cooling medium
circulate on the outside of the tubes. In either case, after
removal of heat from the stream by condensation and removal of the
water vapor, the residual oxygen, nitrogen and uncondensed water
vapor are returned to the autoclave through conduit 34. The
condensate discharged through conduit 36 is not returned directly
to the autoclave since this water is removed from the system in
order to increase the copper concentration in the slurry. It will
be recognized that removal of heat by use of condenser 30 avoids
the loss of oxygen from the system.
In a preferred embodiment it is desired to reduce the iron content
of the final leach liquor to less than about 5 grams per liter. In
order to accomplish this it is necessary that virtually all of the
iron be precipitated as Fe.sub.2 O.sub.3 (equation 3). However, as
noted in equation (3), this reaction is reversible; therefore to
insure the reaction proceeding to the right and obtaining the
greatest amount of iron removal possible, it is necessary to remove
some of the sulfuric acid, H.sub.2 SO.sub.4, the presence of which
tends to cause the reaction to stop or to proceed to the left.
To accomplish partial removal of the acid the slurry is treated by
the introduction into compartment 10D through conduit 38 of a
neutralizing agent. Neutralizing agents such as the oxides,
hydroxides, or carbonates of sodium and potassium, or the oxides,
hydroxides or carbonates of the alkaline earth metals calcium,
strontium, barium and magnesium may be used. In addition, ammonia,
ammonium hydroxide or ammonium carbonate may be used as the
neutralizing agent. In my preferred embodiment I use calcium
carbonate, i.e., limestone.
The limestone may be added as a dry powder or in the form of an
aqueous slurry. The subsequent neutralization reaction proceeds as
follows with the precipitation of CaSO.sub.4 (anhydrite) and the
evolution of gaseous CO.sub.2 :
the downwardly extending baffles 16, 18 which isolate the vapor
space above the liquid level of compartment 10D from the vapor
space above the liquid level in the remaining compartments prevent
contamination or dilution of the oxygen-water vapor atmosphere with
the evolved carbon dioxide and permit removal of this carbon
dioxide through conduit 40 without any loss of oxygen since only
water vapor accompanies the CO.sub.2 as it is discharged through
conduit 40. This loss of water vapor, however, is desirable since
it contributes to further increase the concentration of copper in
the leach liquor and to remove heat. The CO.sub.2 -water vapor
bleed stream in conduit 40 may be vented to the atmosphere or
processed for reclamation of heat.
The slurry next flows into compartments 10E and 10F, consecutively.
While in these compartments the further final hydrolysis of
Fe.sub.2 (SO.sub.4).sub.3 and concomitant precipitation of Fe.sub.2
O.sub.3 take place (equation 3). Also, since the vapor space above
these compartments is connected to that above compartments 10A, 10B
and 10C by conduit 20, the vapor space above compartments 10E and
10F has an atmosphere containing oxygen for oxidizing any material
not oxidized in earlier compartments. Two streams may be taken from
compartment 10F. A purge stream may be vented to the atmosphere
through conduit 42 principally to prevent a buildup of nitrogen gas
which may accompany the feed of oxygen into the autoclave through
conduit 26. A small quantity of oxygen may be removed during this
purging of nitrogen gas. In addition water vapor will be removed
during the purging operation, further increasing the concentration
of copper in the leach liquor. A product slurry stream made up of a
leach liquor (composed principally of an acidic solution of
CuSO.sub.4) and a mixture of solids (principally CaSO.sub.4,
Fe.sub.2 O.sub.3 and gangue) is removed through conduit 44.
The autoclave system of this invention may also be used to
oxidize-leach nickel concentrates which may also contain cobalt, or
concentrates which contain cobalt, nickel and copper. The process
conditions may be somewhat different, but the system can still be
employed. The design features of the autoclave are such that
operating temperatures as high as about 500.degree.F, operating
pressures as high as about 1000 psig, and an acidic environment can
be withstood. The autoclave system of this invention requires a
plurality of compartments. The purpose of these compartments is to
allow sufficient time for the oxygen-containing gas and the slurry
to react so that substantially all of the nonferrous metal in the
slurry is solubilized to the sulfate condition and the sulfur in
the ore in excess of that necessary to form these sulfates reacts
to form sulfuric acid. The number and size of compartments will
depend on such process considerations as retention time,
composition of ore feed, acidity of leach liquor, etc. In general,
enough compartments should be provided to assure substantially
complete reaction of the oxygen with the slurry. Preferably three
or more compartments are used.
The position in the system of the compartment having the isolated
vapor space will depend on various considerations. In general, this
compartment may be placed anywhere in the system. Where
chalcopyrite concentrates are treated, this compartment is
preferably towards the end of the system, but usually is not the
last compartment. The isolated vapor space could, if desired,
extend over more than one slurry compartment of the autoclave. In
such instances conduit 20 would then bypass more than one
compartment. A plurality of isolated vapor spaces could be used if
desired. Such would be the case if the leach liquor fed to the
autoclave were a fairly strong recycle solution and process
considerations required two or more neutralizations during
processing in order to reduce the acidity of the slurry to a level
where iron in the slurry will precipitate out as insoluble iron
oxide.
It is not necessary that all of conduit 20 be located inside
compartment 10D, as indicated in the figure, or even inside the
autoclave. The greater part of conduit 20 could, for example, be
located outside the autoclave compartments as long as its inlet and
outlet connect the compartments adjacent to the compartment having
the isolated vapor space. Also, it is not always necessary that
conduits 40 and 42 have a common outlet as shown in the drawing.
They could, if preferred, be two separate conduits discharging at
two different locations, provided the individual exiting pressures
are reasonably balanced to maintain the slurry at a normal
level.
Should low-cost lime be available for neutralizing, or if a
neutralizing agent is used that does not produce a gaseous reaction
product while lowering the acid level of the slurry, conduits 40
and 42 should have a common outlet so that, through conduit 40, the
pressure in compartment 10D is maintained substantially equal to
the pressure in the rest of the system via conduit 42.
The position in the system of condenser 30 is not critical. At
least a portion of the water vapor which makes up the stream
flowing through conduit 28 should be condensed. Uncondensed water
vapor and other gases (principally oxygen and nitrogen) are
returned to the autoclave through conduit 34 to use their oxygen
content. A blower 46 may be positioned between condenser 30 and the
autoclave. The heat transferred to the cooling water of the
condenser 30 may, optionally, be recovered in the form of
low-pressure steam. In some instances the water removing-heat
removing condenser of this invention may be used to handle the
vapors from more than one autoclave or more than one autoclave
system. For example, in a large commercial operation it may be
desirable to operate with several autoclave systems in parallel. In
such case only one condenser of the type described may be used to
handle the vapors of the several autoclave systems with several
lines corresponding to conduit 34 being individually controlled for
returning oxygen to the system.
EXAMPLE
The operation of the autoclave system of this invention may be
illustrated by the following example:
A copper concentrate containing chalcopyrite (CuFeS.sub.2) is fed
to the autoclave system of the figure in an amount sufficient to
provide about 289 tons of reacted CuFeS.sub.2. This results in the
dissolution of about 100 tons of Cu in the autoclave system. The
concentrate, and 2,000 tons of water at about 80.degree.F, are fed
to the system as a slurry through conduit 24. This slurry flows
consecutively, over the baffles 12, through compartments 10A
through 10F. The temperature and pressure in the autoclave 10 are
maintained at 425.degree.F and 445 psig, respectively. Initially
sufficient oxygen is supplied to react with the contents of the
autoclave and result in an oxygen partial pressure within the
autoclave of about 104 pounds per square inch. Thereafter, for each
100 tons of dissolved copper, commercial grade oxygen (about 99%
O.sub.2) is fed through conduit 26 in the amount of 222 tons of
O.sub.2 and 2 tons of N.sub.2. Limestone in the form of a water
slurry at 80.degree.F is fed through conduit 38 in the amount of
140 tons of CaCO.sub.3. Slurry water fed through conduit 38 amounts
to 140 tons.
Gases from the space above the compartments 10A, 10B, 10C, 10E, and
10F are removed through conduit 28 and conduit 42, and gases from
compartment 10D are removed through conduit 40. The gases removed
through conduit 42 amount of 8 tons of O.sub.2, 2 tons of N.sub.2
and 14 tons of water vapor; those removed through conduit 28 amount
to 1,800 tons of O.sub.2, 450 tons of N.sub.2 and 3,160 tons of
water vapor; and those removed through conduit 40 amount to 60 tons
of CO.sub.2 and 60 tons of water vapor. About 316 tons of water
vapor are condensed and removed through conduit 36 in water-cooled
condenser 30. About 6,350 tons of cooling water flow through
condenser tubes 32 in this operation. Inlet water temperature is
90.degree.F and outlet water temperature is 150.degree.F. About
1,800 tons of O.sub.2 and 450 tons of N.sub.2 together with 2,844
tons of uncondensed water vapor return to the system through
conduit 34. A blower 46 is used for moving these gases, as
indicated in the figure.
From the autoclave system of the figure the oxidized product slurry
is removed through conduit 44 and indirectly cooled to 320.degree.F
in an indirect heat exchanger (not shown), and then flashed to
atmospheric pressure and 230.degree.F. The flashing operation
removes 190 tons of water out of the 1750 tons leaving the
autoclave with the slurry.
The heat balance for this example is summarized below, in millions
of BTU (Reference Temperature: 32.degree.F):
Input streams (solids, gases and water) +220MM BTU Heat of Reaction
(289 tons of CuFeS.sub.2) +2250 Heat removed by condenser -760 Heat
removed through conduits 40 and 42 -180 Heat removed by indirect
slurry cooler (not shown) -420 Heat removed by flashing (not shown)
-440 Heat in Exiting Slurry at 230.degree.F +67 MM BTU
While the above example utilizes CaCO.sub.3 as the neutralizing
agent, it will be understood by those skilled in the art that an
equivalent amount of any of the following neutralizing agents may
be used in place of the CaCO.sub.3 and that any gaseous reaction
product resulting from the reaction thereof with the slurry may be
removed through conduit 40: ammonia, ammonium hydroxide, ammonium
carbonate and the oxides, hydroxides and carbonates of sodium and
potassium and of the alkaline earth metals. calcium, strontium,
barium and magnesium.
While the invention has been described in its preferred form as
including apparatus and process steps relating to the removal, by
the introduction of a neutralizing agent, of some of the sulfuric
acid formed in the oxidation-leaching operation, it will be
understood that this neutralizing step, and the apparatus for
accomplishing it, may be omitted, and the oxidation-leaching
operation may be performed utilizing the described temperature
control aspects of the invention without also performing the
neutralizing step.
The terms and expressions which have been used here are used as
terms of description and not of limitation, and there is no
intention, in the use of such terms and expressions, of excluding
equivalents of the features shown and described, or portions
thereof, it being recognized that various modifications are
possible within the scope of the invention claimed.
* * * * *